A combined epidemiological, cytogenetic and pathological study of spontaneous abortions is proposed. This study will investigate the possible effects of six environmental factors (including epidemicity, recent infection, irradiation, smoking, alcohol and drugs) on the risk of spontaneous abortion and on the risk of abnormalities in the abortus. It will examine a model of spontaneous abortion as a screening mechanism in the reduction of birth defects and the effects of environmental factors on that mechanism.